Process for producing decorative material

ABSTRACT

A coating composition which includes an ionizing radiation-polymerizable oligomer, an ionizing radiation-polymerizable monomer and a releasing agent. The composition has a viscosity regulated to 1000 cps or less, can be rapidly and continuously produced and has excellent surface characteristics. A process for forming a decorative material using the coating composition is also disclosed.

This is a division of application Ser. No. 07/738,634 filed Jul. 31,1991, U.S. Pat. No. 5,271,988.

BACKGROUND OF THE INVENTION

The present invention relates to a coating composition. Moreparticularly, the present invention is concerned with an ionizingradiation curing coating composition suitable as a coating compositionfor use in the interior finishing of buildings and in the surfacedecoration of furniture and various cabinets, and is also concerned witha decorative material, such as a decorative sheet, formed through theuse of the composition.

The conventional decorative paper for use in the interior finishing ofbuildings and in the surface decoration of furniture and variouscabinets is predominantly one produced, for example, by subjecting apaper to moire printing and coating a urethane coating composition onthe moire-printed surface so as to form a top coating layer. Such aurethane-coated paper exhibits relatively superior surfacecharacteristics. It, however, often requires several days for the curingof the coating in the manufacturing process to thereby causemanufacturing disadvantages, and the abrasion resistance and the solventresistance thereof are not always satisfactory.

On the other hand, a method for forming a coating through the use of anionizing radiation curing resin is also known. For example, a decorativepaper can be efficiently produced by printing a pattern on a base paper,coating or impregnating the printed paper with an electron beam curingresin composition of an acrylate resin etc. and irradiating the coatedor impregnated paper with an electron beam for curing (see, for example,Japanese Examined Patent Publication (Kokoku) No. 1-55991). However, theconventional ionizing radiation curing coating compositions as mentionedabove are not always satisfactory in the properties of the formedcoating.

It is generally required that the decorative material for use in theinterior finishing of buildings and in the surface decoration offurniture and various cabinets be excellent not only in the abrasionresistance of the coating film surface but also in such characteristicsas chemical resistance, cellophane adhesive tape resistance and stainresistance. Further, with respect to the manufacturing process of adecorative material as well, an important factor is that they areadvantageous also in simplification of process steps, efficiency andeconomy.

However, actually, no conventional coating composition for use in adecorative material is excellent in both coating film characteristicsand operation facility for a manufacturing process.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above described priorart, and an object of the present invention is to provide a coatingcomposition which can be produced by an efficient, continuousmanufacturing process and which gives a coating film excellent insurface characteristics, and to provide a decorative material using thecomposition.

The coating composition of the present invention is an ionizingradiation curing coating composition comprising a combination of anionizing radiation-polymerizable oligomer with an ionizingradiation-polymerizable monomer and, added thereto, a surface lubricant,said composition having a viscosity regulated to 1000 cps or less.

Further, the decorative sheet of the present invention is characterizedin that it is produced by coating the above-described coatingcomposition on a base material and irradiating the resultant coatingwith an ionizing radiation to cure the coating.

Still further, the decorative plate of the present invention ischaracterized by comprising the above-described decorative sheet havinga plate bonded through an adhesive layer to the back (side on which nocoating composition layer is formed) of the base material of thedecorative sheet.

Still further, the process for producing the decorative sheet accordingto the present invention comprises coating the above-described ionizingradiation curing coating composition preferably in the absence of asolvent to form a composition layer and irradiating the compositionlayer with an ionizing radiation to cure the composition layer.

In the coating composition of the present invention, the surfacelubricant, such as silicone acrylate, is present therein in a dispersedform. Further, the viscosity of the composition is regulated within apredetermined range. These contribute to rapid, desirable formation of acomposition layer on a base material and to appropriate localization ofthe surface lubricant dispersed in optimum conditions on the surface ofthe composition layer after the coating. As a result, the formed coatinghas excellent surface characteristics, especially, cellophane adhesivetape resistance.

Moreover, the coating composition of the present invention has aviscosity regulated within a predetermined range and can be coated inthe absence of a solvent. Accordingly, a troublesome solvent removal(drying) step can be avoided, and advantages are ensured in operation,safety and economy as well.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The ionizing radiation-polymerizable oligomer for use in the ionizingradiation curing coating composition of the present invention greatlycontributes to an improvement in the physical properties especiallyhardness, adhesion and electrical properties after curing and chemicalresistance. From this viewpoint, an acrylate prepolymer having amolecular weight of from 1000 to 3000 is preferably used. Representativeexamples of the prepolymer include polyester acrylate, epoxy acrylate,polyurethane acrylate, polyether acrylate, oligoacrylate, alkyd acrylateand polyol acrylate. From the viewpoint of reducing the viscosity andreducing the cost, a polyester acrylate is particularly preferred.

On the other hand, in the choice of an ionizing radiation-polymerizablemonomer, consideration must be made in the following respects: (1) lowviscosity, (2) high solubility, (3) low volatility, especially thetemperature instantaneously rises at the EB curing), (4) presence of atleast two functional groups, and (5) high safety such as less skinirritation. From this viewpoint, an acrylate or methacrylate monomerhaving a molecular weight of from 100 to 400 is preferably used as theionizing radiation-polymerizable monomer in the present invention.Particularly preferred examples of such monomers include 1,6-hexanedioldiacrylate, dipropylene glycol diacrylate, tripropylene glycoldiacrylate and trimethylolpropane triacrylate.

The mixing proportions of the above described oligomer and monomer areappropriately chosen according to the types thereof. Generally, however,it is preferred that the mixing proportions of the oligomer and themonomer be chosen so as to be at least 5% by weight and up to 95% byweight, respectively. When a polyester type is employed, it ispreferred, for example, that about 70 parts by weight of a monomer bemixed per 100 parts by weight of an oligomer.

When the mixing proportion of the monomer is excessively low, theviscosity is disadvantageously increased to bring about a lowering ofleveling, thereby causing the high-speed coating to be unfeasible andcausing the productivity to be low. On the other hand, when the mixingproportion of the monomer is excessively high, fuming occurs at the timeof curing reaction (for example, at the time of EB irradiation) tosuffer from drawbacks, such as filament degradation. This is alsounfavorable from the viewpoint of manufacturing environment.

In the coating composition of the present invention, a surfacelubricant, such as silicone acrylate, is present in a dispersed state inthe above-described combination of an ionizing radiation-polymerizableoligomer with an ionizing radiation-polymerizable monomer.

Generally, it is required that the decorative sheet for use as abuilding material be excellent in (1) cellophane adhesive taperesistance, (2) solvent resistance, (3) heat resistance, (4) abrasionresistance, (5) chemical resistance, (6) stain resistance, and (7) waterresistance. The properties of the above items (2) to (7) can be madesatisfactory to a certain extent by choosing appropriate types ofoligomer and monomer from those as mentioned above. However, withrespect to the cellophane adhesive tape resistance property of the aboveitem (1), satisfactory results cannot be obtained by only choosingappropriate types of oligomer and monomer. In order to improve thecellophane adhesive tape resistance, it is requisite that the surfaceenergy of the coating film surface be minimized to thereby suppress thesticking property of the tape. The present inventors have found that animprovement of the cellophane adhesive tape resistance without detrimentto the properties of the above items (2) to (7) can be attained bycoating and curing a composition in which a surface lubricant, such assilicon acrylate, is present in a dispersed form, especially in the formof an emulsion dispersion.

Preferably employed as such a silicone acrylate are those satisfying thefollowing conditions:

molecular weight:

from 500 to 10,000, preferably from 2,000 to 4,000,

functional group equivalent (molecular weight/number of functionalgroups):

from 400 to 8,000, preferably from 500 to 2,000, and

type of functional group:

preferably, a methacryl group, an acryl group and a mercapto group,especially when an EB curing (electron beam irradiation) iscontemplated.

In the present invention, the above-described silicone acrylate may bepresent as it is in the above-described mixture of an oligomer and amonomer. Alternatively, some proportion of the silicone acrylate mayform a copolymer with the above-described oligomer or monomer. Thisaspect is also encompassed by the present invention.

The content of the above-described silicone acrylate is preferably up to5% by weight, more preferably from 0.1 to 3.0% by weight, and mostpreferably from 0.5 to 2.0% by weight. As mentioned above, theimprovement of cellophane adhesive tape resistance and the improvementof leveling by the addition of the surface lubricant are likely tocountervail each other. However, a coating film excellent in both ofcellophane adhesive tape resistance and leveling (namely, there is nopin hole) can be obtained by choosing the above-described siliconeacrylate as a surface lubricant and regulating the amount thereof withinthe above-described range.

For the coating composition of the present invention, it is important toregulate the viscosity to 1000 cps or less from the viewpoint ofincreasing the coating speed, the transferability of the above-describedsurface lubricant in the composition and the localization of thelubricant onto the surface of the coating film. Also, appropriateregulation of the viscosity within a preferred range is desired inaccordance with the coating method employed. For example, when gravurecoating is employed, it is preferred to regulate the viscosity to avalue much lower than 1000 cps, for example, 400 cps or less at roomtemperature. Such regulation of the viscosity can be accomplished byheating the coating composition and the coating apparatus for applyingthe coating composition or by varying the mixing proportion of monomercomponent as mentioned above.

A matting agent comprised of a particulate material having a particlesize of from 0.1 to 30 μm, preferably from 10 to 20 μm, may be added tothe coating composition of the present invention for the purpose ofproviding a matted coating film. Suitable examples of the matting agentinclude particles of an inorganic material, such as silica and asilicone resin (powder and beads), and powder and beads of an organicmaterial, such as a crosslinked alkyl, a crosslinked styrene, aninzoguanamine resin, a urea-formaldehyde resin, a phenolic resin,polyethylene and a nylon. The matting agent is added in an amount ofpreferably from 0.5 to 40% by weight, more preferably from 5 to 30% byweight.

Moreover, the coating composition of the present invention may becolored by adding a pigment or a dye in an amount which does not inhibitthe curing of the composition.

A solvent may be added to the coating composition of the presentinvention. The addition of a solvent is not always necessary, and at thetime of coating as well, it is not necessary to use a solvent.Accordingly, because the coating composition of the present inventionhas a viscosity regulated within a predetermined range and can be coatedin the absence of a solvent, a troublesome solvent removal (drying) stepcan be avoided and advantages are ensured in operation, safety andeconomy.

The method of producing a decorative material by the use of theabove-described coating composition will now be described.

Suitably employed as a base material in the manufacturing of adecorative sheet, such as a decorative paper, are paper materials, suchas a titanium paper, a tissue paper, a kraft paper, a pulpboard, apaperboard, a gypsum board paper and a synthetic paper, each having abasis weight of about 20 to 300 g/m², and also, besides paper materials,cloth and various types of coated papers.

The coverage of the coating composition is appropriately chosen inaccordance with the property of the base material and the object, whichis preferably in the range of from 3 to 60 g/m².

The curing is performed by means of an ionizing radiation, such asultraviolet rays and electron beams. When the curing is performed bymeans of electron beams, the EB intensity is desirably in the range offrom 2 to 15 Mrad, especially from 3 to 5 Mrad. When the intensity isless than 2 Mrad, poor curing unfavorably occurs due to the doseshortage. On the other hand, when the irradiation is performed at anintensity exceeding 15 Mrad, degradation of the base material isunfavorably caused by the excess dose, which is causative of basematerial breakage and rupture (for example, at the time of winding orfurther lamination to a plate).

In particular, when use is made of a base sheet, such as paper, intowhich the coating composition easily permeates, electron beams arepreferred among ionizing radiations. In the case of ultraviolet rays,permeation of the composition into the base material is difficult andthe curing of the coating composition is insufficient in the basematerial. Further, in the case where a pigment or the like is added tothe coating composition, ultraviolet rays are likely to be absorbed bythe pigment or the like to thereby cause the curing to be insufficient.Accordingly, in such cases, the use of electron beams is preferred.

Efficient, continuous production of a decorative sheet is feasible bythe employment of the above-described coating and curing methods.

When the curing is performed by the irradiation of ultraviolet rays, itis preferred to add a photoinitiator and/or a sensitizer to the coatingcomposition. The photoinitiator absorbs ultraviolet rays and initiates apolymerization reaction. Conventional carbonyl compounds, sulfurcompounds, azo compounds and organic peroxides may be used as thephotoinitiator. The sensitizer may be used in combination with thephotoinitiator for attaining improved effects. Conventional amines,sulfur compounds, nitriles, phosphorus compounds, chlorine compounds andnitrogen compounds may be used as the sensitizer.

In the decorative material of the present invention, a print layer and apattern layer may be previously formed on the surface of the basematerial, and also a filling layer may be formed thereon.

A resin exhibiting a good adhesion to the base material and having astrong cohesive strength should be chosen as a vehicle of an ink for usein the formation of a pattern layer. The reason is presumed to be thatas the ionizing radiation curing coating composition of the presentinvention suffers from rapid shrinkage at the time of curing, if an inkhaving poor adhesion to the base material is used, microscopicallypartial peeling occurs between the ink and the base material due to theshearing stress generated at the interface of the ink and the basematerial by the curing shrinkage to thereby cause the cellophaneadhesive tape resistance of the coating film to be markedly lowered.

Preferably employed as a vehicle when paper is used as a base materialare a water soluble salt of acryl, a urethane and a mixture of aurethane and a copolymer of vinyl chloride and vinyl acetate.

It has been found that a fibrous vehicle, such as cellulose nitrate,provides no satisfactory cellophane adhesive tape resistance.

Further, depending upon the purpose, the above-described decorativesheet is integrally bonded to the surface of a member to be decorated,for example, a wood product through an adhesive.

The process for producing a decorative sheet having uneven portionsformed in synchronism with the pattern through the use of thecomposition of the present invention will now be described.

In preparing a decorative sheet having synchronized uneven portions, aliquid repellent pattern layer is first formed on a base sheet, theabove described coating composition of the present invention is coatedon the pattern layer, a recessed portion is formed in the coating layerformed on the surface of the above-described pattern layer throughliquid repellent action between the formed liquid repellent patternlayer and the coating layer. The formed coating layer is irradiated withan ionizing radiation to cure the coating layer having uneven portionsin synchronism with the above-described pattern layer, thereby preparinga decorative sheet having uneven portions formed in synchronism with thepattern.

In order to form the above described liquid repellent pattern layer, itis possible to use the conventional printing techniques, such as gravureprinting and silk screen printing. The following inks may be used as theliquid repellent ink.

(1) A liquid repellent ink comprising a binder having in itself a liquidrepellency and, added thereto, a pigment, dye, etc.

Examples of the binder resin used in this case include fluororesins,such as polyvinylidene fluoride and polyvinyl fluoride, and siliconeresins, such as polysiloxane and silicone acrylate. In particular, useare made of binder resins satisfying the following requirement:

critical surface tension of binder<surface tension of coatingcomposition (in liquid state)

(2) An ink comprising a binder not having in itself a liquid repellencyand, added thereto, a liquid repellent substance and further a pigment,dye, etc.

Examples of the liquid repellent substance usable in this case includeresins, such as silicone resins, fluororesins, substances described inthe above item (1), polyethylene and polypropylene, and waxes. Further,in this case, aminoalkyd resins etc. may be used as the binder.

(3) An ink comprising a binder having in itself a liquid repellency and,added thereto, a liquid repellent additive and further a pigment, etc.

EXAMPLE 1

An electron beam curing coating composition comprising the followingcomponents was prepared.

polyester acrylate (manufactured by Morohoshi Ink Co., Ltd., Japan) 60parts by weight

trimethylolpropane triacrylate (manufactured by Toagosei ChemicalIndustry Co., Ltd., Japan) 10 parts by weight

1,6-hexanedioldiacrylate (manufactured by Nippon Kayaku Co., Ltd.,Japan) 29 parts by weight

silicon acrylate (MEB-1 manufactured by The Shin-Etsu Chemical Co.,Ltd., Japan) 1 part by weight

Separately, a moire pattern was printed on a reinforced paper (30 g/m² ;a product of Sanko Paper Manufacturing Corp., Japan) as a base materialby means of a rotogravure printing machine through the use of an acrylicink (HAT manufactured by Morohoshi Ink Co., Ltd.).

Thereafter, the above described coating composition was coated on theabove-described base material having a moire print. The properties,particularly viscosity, of the above-described coating compositionbefore coating and the dispersed state of silicone acrylate were asfollows.

    ______________________________________                                        Viscosity:                                                                           Temp. (°C.)                                                                     cps                                                           ______________________________________                                               25       100                                                                  30       95                                                                   40       70                                                                   50       55                                                                   60       35                                                                   70       25                                                            ______________________________________                                    

Dispersed State

Suspension with partial dissolution.

The above described coating composition was coated at a coverage of 12g/m² by gravure direct coating. The line speed was 100 m/min.

The coated product was then irradiated with an electron beam to cure thecoating layer. The electron beam irradiation was conducted under thefollowing conditions through the use of a scanning electron beamirradiator.

accelerating voltage: 175 kV

beam current: 183 mA

electron beam: 5 Mrad

The decorative sheet having a moire pattern thus obtained was a sheet ofmirror finish having a good gloss on its surface [75° mirror state(JISZ8741): 100]. The obtained decorative sheet was integrally bonded toan MDF plate by means of vinyl acetate adhesive (AC500 manufactured byChuo Rika Kogyo Corp., Japan) to prepare a decorative plate.

The decorative plate was subjected to tests on the cellophane adhesivetape resistance (tape delamination test), solvent resistance, abrasionresistance and stain resistance. The tests were conducted by thefollowing methods.

Cellophane Adhesive Tape Test

Peeling was conducted by means of a Nichiban tape (40° C.±3° C., after 2hr) according to the standard for printed plywood-colored plywood(established by Printed and Colored Plywood Association of Japan) toobserve the surface appearance.

Solvent Resistance Test

The surface of the decorative sheet was coated with thinner (JISK5538)and rubbed under a load of 500 g to observe the damage to the coating bythe solvent according to the above-described standard.

Abrasion Resistance Test

Abrasion test was conducted through the use of two soft abrasion ringsunder a load of 1 kg according to the standard for JAS Abrasion C Testto observe the state of damage to the coating.

Stain Resistance:

Lines having a size of 10 m/m width were formed on the surface of thecoating through the use of an oil base ink, a water base ink and acrayon, allowed to stand for 4 hr and wiped off, and the state ofstaining was then observed (JAS Stain A Test).

The results of various characteristic tests are given in the followingTable 1.

EXAMPLE 2

An electron beam curing coating composition comprising the followingcomponents was prepared.

polyester acrylate (manufactured by Morohoshi Ink Co., Ltd.) 60 parts byweight

trimethylolpropane triacrylate (manufactured by Toagosei ChemicalIndustry Co., Ltd.) 10 parts by weight

1,6-hexanedioldiacrylate (manufactured by Nippon Kayaku Co., Ltd.) 19parts by weight

silicone acrylate (MEB-1 manufactured by The Shin-Etsu Chemical Co.,Ltd.) 1 part by weight

silica powder (manufactured by Catalysts and Chemicals Industries Co.,Ltd.) 20 parts by weight

Separately, a moire pattern was printed on a reinforced paper (30 g/m² ;a product of Sanko Paper Manufacturing Corp.) as a base material bymeans of a rotogravure printing machine through the use of an acrylicink (HAT manufactured by Morohoshi Ink Co., Ltd.).

Thereafter, the above-described coating composition was coated on theabove-described base material having a moire print. The properties,particularly viscosity, of the above-described coating compositionbefore coating and the dispersed state of silicone acrylate were asfollows.

    ______________________________________                                        Viscosity:                                                                           Temp. (°C.)                                                                     cps                                                           ______________________________________                                               40       550                                                                  70       165                                                           ______________________________________                                    

Dispersed State

Suspension with partial dissolution.

The above described coating composition was coated at a coverage of 12g/m² by gravure direct coating. The line speed was 100 m/min.

The coated product was irradiated with an electron beam to cure thecoating layer. The electron beam irradiation was conducted under thefollowing conditions through the use of a scanning electron beamirradiator.

accelerating voltage: 175 kV

beam current: 183 mA

electron beam: 5 Mrad

The decorative sheet having a moire pattern thus obtained was a sheet ofmirror finish having a good gloss on its surface [75° mirror state(JISZ8741): 40]. The obtained decorative sheet was integrally bonded toan MDF plate by means of a vinyl acetate adhesive (AC500 manufactured byChuo Rika Kogyo Corp.) to prepare a decorative plate.

The decorative plate was subjected to tests on the cellophane adhesivetape resistance (tape delamination test), solvent resistance, abrasionresistance and stain resistance. The results are given in the followingTable 1.

COMPARATIVE EXAMPLE 1

A decorative plate was prepared in the same manner as that of Example 1,except that use was made of a coating composition comprising thefollowing components and subjected to a test on its characteristics. Theresults are given in the following Table 1.

acryl polyol 60 parts by weight

modified silicone oil 2 parts by weight

amide wax 1 part by weight

tolylene diisocyanate 15 parts by weight

toluene 7 parts by weight

ethyl acetate 15 parts by weight

                  TABLE 1                                                         ______________________________________                                                   Ex. 1   Ex. 2     Comp. Ex. 1                                      ______________________________________                                        cellophane   free from free from free from                                    adhesive tape                                                                              peeling   peeling   peeling                                      resistance                                                                    solvent      not less  not less  not less                                     resistance   than 100  than 100  than 100                                                  times     times     times                                        abrasion     free from free from pattern lost                                 resistance   loss of   loss of                                                             pattern   pattern                                                stain resistance                                                                           no stain  no stain  no stain                                     *) steel woolen                                                                            ∘                                                                           ∘                                                                           x                                            property                                                                      ______________________________________                                         Note: *) ∘: good x: poor                                     

What is claimed is:
 1. A process for producing a decorative sheet,comprising the steps of:coating an ionizing radiation curing coatingcomposition comprising an ionizing radiation-polymerizable oligomer, anionizing radiation-polymerizable monomer and a releasing agent, saidcomposition having a viscosity regulated to 1000 cps or less, on a basematerial to form an ionizing radiation curing coating composition layer;and irradiating the coating composition layer with an ionizing radiationto cure the coating composition layer.
 2. A process according to claim1, wherein said ionizing radiation is an electron beam and theirradiation is conducted at a dose of 2 to 15 Mrad.
 3. A process forproducing a decorative sheet having uneven portions formed insynchronism with a pattern, comprising the steps of:forming a liquidrepellent pattern layer on a base sheet; coating said pattern layer witha coating composition comprising an ionizing radiation-polymerizableoligomer, an ionizing radiation-polymerizable monomer and a releasingagent, said composition having a viscosity of no greater than 1000 cps;forming a recessed portion in the coating layer formed on the surface ofthe pattern layer through liquid repellent action between the formedliquid repellent pattern layer and the coating layer; and irradiatingthe coating layer with an ionizing radiation to cure the coating layerhaving uneven portions in synchronism with the pattern of the patternlayer.
 4. A process for producing a decorative sheet having unevenportions formed in synchronism with a pattern, comprising the stepsof:forming a liquid repellent pattern layer on a base sheet; coatingsaid pattern layer with a coating composition comprising an ionizingradiation-polymerizable oligomer, an ionizing radiation-polymerizablemonomer and a releasing agent comprising a silicone acrylate having amolecular weight of 1000 to 10000 and a functional group equivalent ofno greater than 2000, said composition having a viscosity of no greaterthan 1000 cps; forming a recessed portion in the coating layer formed onthe surface of the pattern layer through liquid repellent action betweenthe formed liquid repellent pattern layer and the coating layer; andirradiating the coating layer with an ionizing radiation to cure thecoating layer having uneven portions in synchronism with the pattern ofthe pattern layer.